Turbine buckets



Feb.\18, 1958 D. GERDAN ETAL 2,823,892

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TURBINE BUCKETS 4 Sheets-Sheet 4 Filed June 9, 1952 5 mgm; w wwf, m mam, m ff; A :a 6W? V WM 4Z .m5 @n TURBINE EUCKETS Dimitrius Gordan and Stuart Wilder, Jr., Indianapolis, Ind., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application .lune 9, 1952, Serial No. 292,545

24 Claims. (Cl. 253-3915) Our invention relates to fluid-directing elements for turbomachines such as are generally known by the terms buckets, blades and vanes and, more particularly, to those which are adapted for use in axial flow cornpressors or turbines of known type.

The invention has particular relation to turbines of high temperature types, since one of the primary objects of the invention is to provide a bucket or the like which is particularly adapted for cooling.

it is generally recognized that the principal factor limiting the efficiency and power output of gas turbines is the limited temperature of the motive iluid imposed by the turbine buckets. It has long been realized that adequate provision for cooling turbine buckets could be beneficial either in increasing the temperature limitation of the engine or in permitting reduced use of critical materials, or both. As a result, many proposals tor structures adaptable for cooling have been advanced and some have been used to some extent. Despite the long period of awareness of the need for a satisfactory cooled bucket, progress in this respect has not been satisfactory.

The principal objects `of our invention are to provide a turbine bucket or the like having superior characteristics so far as cooling is concerned, which is of high strength, and, moreover, one which is readily adapted to simple production techniques.

This result is attained by the use of sheet metal for the major portion, if not all, of the bucket. A particular feature of the invention is the utilization of laminated sheet metal construction for the major part of the bucket, the laminae being so disposed as toprovide channels for cooling air. The outer surface of the blade, which is the huid-directing portion, may be a tubular sheath of sheet metal of external form governed by the aerodynamic requirements of the installation. In other words, the outer surface of the blade is a sheath of sheet metal which is of generally airfoil form as required and which is mounted over the laminated structure which contributes strength and stiffness to the blade in addition to defining the cooling air passages. By virtue of the invention, cornplicated castings, forgings, or machined shapes are unnecessary and thus the production of blades becomes primarily a matter of sheet metal forming and uniting of the sheet metal parts, which may be performed by high temperature brazing.

The nature of the invention and the advantages thereof will be clearly apparent to those skilled in the art from the succeeding detailed description of the preferred embodiments of the invention.

Referring to the drawings:Fig. 1 is a longitudinal sectional View of one form of turbine bucket in accordance with the invention shown as mounted in a fragmentary portion of a turbine rotor, this section being taken approximately on the mean camber line of the blade; Figs. 2 and 3 are longitudinal sections of the same taken on planes transverse to the turbine axis as indicated by lines`2-f2 and 3-3 in Fig. 1; Figs. 4 and 5 are cross- States Patent() 2,823,892 Patented Feb. 18, 1958 sectional views of the blade taken on the planes indicated by lines 4 4 and 5-5 in Fig. l; Fig. 6 is a plan of a representative lamina illustrating by broken lines suitable locations for tabs vby which the laminae are aligned with suitable spacers between them as needed when stacked for assembly, the tabs being removed in the process of manufacture; Fig. 7 is a cross-sectional View of a second form of turbine bucket in accordance with the invention taken on the plane indicated by line 7 7 in Fig. 8; Fig. 8 is a longitudinal section of the same taken on the plane indicated by line 8--8 in Fig. 7; Fig. 9 is a longitudinal section of a third form of bucket, this section being taken approximately on the mean camber line of the blade; Fig. l0 is a cross-section of the same taken on the plane indicated at line 10-10 of Fig. 9; and Figs. ll and l2 are longitudinal sections taken on the planes ndicated by lines 11-11 and 12-12 in Fig. 10.

Referring first to Figs. 1 to 5, inclusive, the first form of turbine bucket according to the invention comprises a blade portion indicated generally as A and a base or root portion indicated generally vas B. The base portion is lformed with multiple dovetail serrations 11 which engage in mating serrations in `a slot 12 in the rim of a turbine wheel 13. The external form of the base so far described is conventional. The central part of the bottom of the root is spaced from the bottom of the groove to define an air passage or chamber 14 to which cooling air is supplied in any suitable manner as by a passage le through the rim of the turbine wheel. The base portion B is comprised of a block 17 at the leading edge of the wheel, a block 18 at the trailing edge, and a number of laminas 20, which will be more fully described, stacked between the blocks 17 and 18. The outer contours of the blade portion Aare defined. by a sheath 21 formed to appropriate contour from sheet metal and brazed to the laminae which abut it. The sheath 21 may be of any suitable form dictated by the requirements of the installation. Ordinarily, turbine buckets as illustrated are of generally airfoil section, with rather high camber, tapering from the base toward the tip, and twisted, as will be most clearly apparent from Fig. 5. The walls or faces of the sheath define the faces of the blade. The laminae 20 comprise two principal groups; the longer laminae which extend from the top of the chamber 14 into the blade and shorter laminae 23 which terminate at the top of the blade root. The laminae 23 thus serve to space the other laminae and, `as will be most clear from Fig. 4, the laminae 23 are formed of two parts, 23a and 23b, defining respectively the two sides or faces ol' the blade root in which the dovetail grooves are formed, and leaving between them passages 24 by which air is conducted outwardly from the chamber 14. The l-aininae 26 which are disposed between the laminare 23 throughout the central portion of the chord of the blade extend from the chamber 14 to or near the open tip of the blade as defined by the upper end of the sheath 2i.

Particularly where the chord of the blade increases toward the base, and also particularly in a bucket supported only at one end as distinguished from stator vanes which may be supported at both ends, additional laminae 27 and 28 corresponding to the laminae 2o `but progressively shorter so as to extend a lesser distance into the blade may be provided. The laminae 27 and 28 provide additional stitening of the portion of the blade near the base and help to carry the centrifugal load of the sheath 21. The laminae 25, 27, and 28 constitute a core` for the blade portion A, the surface of which is defined by the sheath 21. i

The laminae 26, 27, and 28 are punched as indicated at 29 (Fig. 2) within the base to define a passage 31 extending through the stack of laminations by which lair 3 flow is equalized between the numerous passages between the laminae and also is conducted into slots 32 in the end portions or blocks 17 and 18 of the base (see also Fig. 4) by which air is directed into the spaces 'between the laminae and the leading and trailing edges of the blade.

The manner in which the air or other cooling agent circulates through the blade will be apparent. It is introduced through the passage 16 into the chamber 14, flows through the passages 24 into the chamber 31, and then fiows through the grooves 32 and through the spaces between the laminae 26, 27, and 28 and out the open tip of the blade.

Figs. 7 and 8 illustrate a modified form of bucket which may be similar in every respect to that already described in detail with reference to Figs. 1 to 5, except that additional laminae 36 are interposed between the laminae 26, 27, and 28. As a result, the laminated structure through the blade forms a solid stack, which has some advantages in manufacture and, additionally, the area of the cooling passages is reduced somewhat, which promotes more effective utilization of the coolant. As will be seen, the laminae 36 taper with the blade from base to tip and are approximately one-third as wide as the laminae between which they are stacked. The laminae 23, 26, 27, and 28 and the sheath 21, as well as the blocks 17 and 18, may be identical as those of the other form. Laminae 26, 27, 28, and 36 constitute the blade core in this form.

Referring now to Figs. 9 to 12, a still further form of the invention is illustrated therein which is `distinguished by the staggered arrangement of the laminae extending through the blade so that `all of the laminae extend into the blade, each alternate one engaging opposite faces of the sheath 21. The base parts 17 and 18 and the sheath 21 may be the same as previously described. The central laminae which extend the length of the blade, identified as 46 and 47, lie against the convex and concave faces of the blade sheath 21 respectively, and extend to the chamber 14. Associated with each of these laminae is a base lamina, 46a and 47a, respectively which defines the opposite side of the base from the longer laminae. A channel or slot 48 is defined between the interior faces of the laminae 46 and 46a, and 47 and 47a, respectively. The laminae toward `the leading and trailing edge of the blades, which `are identified as 46 and 47', are progressively shorter to provide a gradualrdecrease in the thickness of the stack but are otherwise similar to the laminations 46 and 47. The inner edges of the laminations may be formed to define a passage 31 through the base, `as in the other form, communicating with the slots 32. Laminae 46, 47, 46', and 47' constitute the blade care in this form.

lt will be seen that the several forms of the invention disclosed have many features in common, but, due to the diversities of the construction, each may have certain advantages in use or in ease of fabrication over others. As will be apparent, the circulation of cooling air through the blade form of Figs. 7 and 8 and that of Figs. 9 to l2 is similar to that described with reference to Fig. 1.

Since the edges of the laminae engage in the dovetail slot and the laminae of the base are stacked together to form a relatively solid structure, a very strong attachment of the base results, adapted to withstand the very high centrifugal stresses encountered in turbines. The laminae not only provide radiating surface and 4air passages, but also serve to stiffen the sheet metal Outer surface of the blade which is subjected to high velocity streams of hot gas. The sheet metal provides a smooth outer surface with a minimum of finishing or polishing, and the light weight of the entire bucket structure reduces the load on the turbine wheel, thereby making it possible to lighten the wheel.

The exibility of the process, that is, its adaptability to buckets o r vanes of various configurations, will be apparent.

The method of manufacture of a typical bucket may be described briefiy. Referring to Fig. 6, a typical lamina, specifically one of the laminae 26 and Fig. l, is illustrated in solid lines. When the laminae are formed by blanking `from sheet metal, normally of a heat resistant type such as stainless steel, the blank includes not only the form which becomes part of the finished bucket but also tabs by which the laminae may be accurately stacked for brazing. Fig. 6 illustrates tabs identified as 61 to 66, inclusive, at various points, each tab being formed with a hole 68 punched therein. Each blank will have ordinarily two or three such tabs at whatever location is appropriate to the form of the particular blank. The laminae are stacked on pins which pass through the openings 68 in the tabs so that they are accurately aligned. A lamina 26 may, for example, have thereon tabs 61 and 64. A lamina 27 could have tabs 62 or 66 and 64. A lamina 23 or 28 might be provided with tabs 63, 64, and 65, etc. The tabs may be notched or scored where they join the body of the laminae so that they can be broken off easily 'after `the laminated structure is completed.

The laminae may be brazed in any suitable manner by providing a high temperature brazing composition be tween the sheets of metal and heating them in a reducing atmosphere while the assembly is held in a suitable fixture. The end pieces 17 and 18 of the base are brazed onto the laminated structure at the same time. A-fter this sub-assembly is completed, the tabs may be broken off, burrs may be removed, and the outer sheath is put on. This sheath, if the form of the blade permits, may be closed at both leading and trailing edges and be slipped over the end of the blade. Alternatively, it may be folded over the laminated core and then be brazed or welded at the leading or trailing edge. Alternatively, the two faces of the sheath may be separate sheets welded or brazed together at both the leading and trailing edges. The sheath is brazed to the edges of the laminae and is brazed or welded to the base of the blade comprising the blocks 17 and 18 and the laminated structure therebetween.

Where the laminae extending into the bucket are spaced from each other, as inthe form of Fig. 1, spacers may be inserted between them until the blade is completed and then the spacers may .be pulled `out.

After these operations have been performed, the base of the blade may be ground or otherwise formed to provide accurate contours to engage the slot in the turbine wheel and the outer surface of the blade portion may be polished.

It will thus be seen that blades according to the invention are easy to make, requiring a minimum of machining and dispensing with involved forging or casting operations. The blocks 17 and 18 may be cast, but are of simple form.

The preferred embodiments of the invention have been described in detail in order to explain the principles of the invention. This description is not to be construed ask limiting the invention, since many variations thereof may be devised by the exercise of skill in the art within the scope of the invention.

As used in the claims the term'wall of the sheath refers to the inner surface of a part of the sheath which denes a face of the blade.

We claim:

1. A huid-directing element for turbomachines and the like, said element comprising a base portion for mounting the element and a blade portion extending from the base portion, the base portion comprising a stack of laminae, the laminae having registering openings therein defining an air passage extending lengthwise of the base, some of said laminae extending into the blade portion to define a core therefor and being mutually spaced over at leastV part of the width of the blade portion to define air conduits communicating with the said passage and extending lengthwise of the blade, the blade portion also comprising an external sheath united with the laminae extending thereinto and with the base portion, the said passage including portions located so as to communicate with the interior `off the blade sheath adjacent the leading and trailing edges thereof.

2. A huid-,directing element for turbomachines and the like, said element comprising a base portion for mounting the element and a blade portion extending from the base portion, the base portion comprising a stack of laminae and relatively thick blocks on each end of the stack, the laminae and blocks having registering openings therein defining an air passage extending lengthwise of the base, some of said laminae extending into the blade portion to define a core therefor and being mutually spaced over at least part of the width of the blade portion to define air conduits communicating with the said passage and extending lengthwise of the blade, the blade portion also comprising an external sheath united with the laminae extending thereinto and with the base portion, the said passage including portions located so as to communicate with the interior of the blade sheath adjacent the leading and trailing edges thereof.

3. A Huid-directing blade for turbomachines and the like, said blade comprising a number of parallel laminae having extension in the directions lengthwise of the blade and from face to face of the blade to define a core for the blade, the blade also comprising a tubular sheath deiining the Huid-directing surfaces thereof, the said coredefining laminae extending through the sheath and being united to the sheath, the walls of the sheath abutting at least some of the laminae, the laminae being mutually spaced to define with the sheath coolant passages extending lengthwise of the blade portion, and at least some of the laminae extending from the sheath to provide means for attaching the blade.

4. A fluid-directing blade as recited in claim 3 in which the laminae defining the core are spaced from each other to define passages extending from wall to wall of the sheath.

5. A Huid-directing blade as recited in claim 3 in which the laminae deiining the core comprise a first mutually spaced set extending from wall to wall of the sheath and a second set interleaved with the first set, the laminae of the second set being spaced from the walls of the sheath to define passages between the edges of the laminae of the second set and the sheath.

6. A `fluid-directing blade as recited in claim 3 in which the laminae defining the core comprise two interleaved sets, the laminae of each set being mutually spaced, the laminae of one set abutting one wall of the sheath and being spaced from the other wall, and the laminae of the other set abutting the said other wall and being spaced from the said one wall.

7. A duid-directing element for turbomachines and the like, said element comprising a blade portion for directing fluid and a base portion for mounting the element, the `element comprising a number of parallel laminae having extension in the directions lengthwise of the element and from face to face of the blade portion, at least some of said laminae extending through the base portion and into the blade portion to define a core for the blade portion, the blade portion also comprising a tubular sheath defining the fluid-directing surfaces thereof and united to the laminae extending thereinto, the walls of the sheath abutting at least some of the laminae, the laminae being mutually spaced to define with the sheath coolant passages extending lengthwise of the blade portion.

8. A fluid-directing element as recited in claim 7 in which the said laminae comprise two sets, the first set being confined to the base portion of the element, and the second set being interleaved with the first set and extending into the blade portion to define passages extending from wall to wall ofthe sheath. t

9. A fluid-directing element as recited in claim 7 in which the said laminae comprise a first mutually spaced set extending from wall to wall of the sheath and a second set interleaved with the first set, the laminae of the second set being spaced from the walls of the sheath to define passages between the edges of the laminae of the second set and the sheath.

l0. A huid-directing element as recited in claim 7 in which the said laminae comprise two interleaved sets, the laminae of each set being mutually spaced, the laminae of one set abutting one wall of the sheath and being spaced 'from the other wall, and the laminae of the other set abutting the said other wall and being spaced from the said one wall.

ll. A fluid-directing element as recited in claim 7 in which the said laminae have registering openings in the base portion defining a coolant passage extending lengthwise of the base communicating with the coolant passages extending lengthwise of the blade portion.

l2. A Huid-directing element for turbomachines and the like, said element comprising a blade portion for directing fluid and a base portion for mounting the element, the element comprising a number of parallel laminae having extension in the directions lengthwise of the element and from face to face of the blade portion, some of said laminae extending through the base portion and through the blade portion to define a core for the blade portion, other of said Vlaminae adjacent the leading and trailing edges of the blade extending 'from the base of the blade only part way to the tip of the blade, the blade portion also comprising a tubular sheath deiining the fluid directing surfaces thereof and united to the laminae extending thereinto, the walis of the sheath abutting at least some of the laminae, the laminae being mutually spaced to -define with the sheath coolant passages extending lengthwise ofthe blade portion.

.13. A fluid-directing element as recited in claim l2 in which the said laminae comprise two sets, the first set being confined to the base portion of the element, and the second set being interleaved with the first set and extending into the blade portion to define passages extending from wall to wall of the sheath.

14. A fluid-directing element as recited in claim l2 in which the said laminae comprise a rst mutually spaced set extending from wall to wail of the sheath and a second set interleaved with the first set, the laminae of lthe second set being spaced from the walls ofthe sheath to define passages between the edges of thel laminae of the second set and the sheath.

l5. A fluid-directing element as recited in claim l2 in which the said laminae comprise two interleaved sets, the laminae of each set being mutually spaced, the laminae of one .set abutting one wall of the sheath and being spaced from the other wall, and the laminae of the other set abutting the said other wall and being spaced from the said one wall.

16. A fiuid-directing blade for turbomachines and the like, said blade comprising a number of parallel iaminae abutting in face-to-face relation and having extension in the directions )engthwise of the blade and from face to face of the blade, at least some of said laminae defining a core for the blade, the blade also comprising a tubular sheath defining the huid-directing surfaces thereof, the said cox'e-dening laminae extending through the sheath and being unitedl to the sheath, the walls c-f the sheath abutting at least some of the laminae, the core-defining laminae being mutually spaced over at least part of the area thereof to define with the sheath coolant passages extending lengthwise of the blade.

17. A iiuid-directing blade as recited in claim l6 in which the laminae defining the core comprise a first mutually spaced set extending from wall to wall of the sheath and a second set interleaved with the first set, the laminae of the second set being spaced from the waits of the sheath to define passages between edges of the laminae of the second set and the sheath.

18. A fluid-directing blade as recited in claim 16 in which the laminae defining the core comprise two -interleaved sets, the laminae of each set being mutually spaced, the laminae of one set abutting one wall of the sheath and being spaced from the other wall, and the laminae of the other set abutting the said other wall and being spaced from the said one wall.

19. A fluid-directing element for turbomachines and the like, said element comprising a blade portion for directing uid and a base portion for mounting the element, the element comprising a number of parallel laminae having extension in the directions lengthwise of the element and from face to face of the blade portion, at least some of said laminae extending through the base portion and into the blade portion to deiine a core for the blade portion, the blade portion also comprising a tubular sheath deiining the duid-directing surfaces and the leading and trailing edges thereof and united to the laminae extending thereinto, the walls of the sheath abutting at least some of the laminae, the laminae being mutually spaced and spaced from the leading and trailing edges of the tubular sheath to define with the sheath coolant passages extending lengthwise of the blade portion, the base portion deiining passages therein to direct air into the coolant passages between the laminae and between the laminae and the leading and trailing edges of the sheath, the said passages in the base portion communicating with the exterior of the base portion and with the said coolant passages.

20. A huid-directing element as recited in claim 19 in which the said laminae comprise two sets, the first set being confined to the base portion of the element, and the second set being interleaved With the first set and extending into the blade portion to define passages extending from wall to wall of the sheath.

2l. A huid-directing element as recited in claim 19 in which the said laminae comprise a rst mutually spaced set extending from wall to wall of the sheath and a second set interleaved with the rst set, the laminae of the second set being spaced from the walls of the sheath to define passages between the edges of the laminae of the second set and the sheath.

22. A fluid-directing element as recited in claim 19 in which the said laminae comprise two interleaved sets, the laminae of each set being mutually spaced, the laminae of one set abutting one wall of the sheath and being spaced from the other Wall, and the laminae of the other set abutting the said other wall and being spaced from the said one Wall.

23. A huid-directing blade for turbomachines and the like, said blade having a duid-directing portion and comprising a number of physically united laminae having extension in the directions lengthwise of the blade and from face to face of the blade, some of said laminae extending through the Huid-directing portion of the blade and extending beyond one end of the fluid-directing portion of the blade to provide means for attaching the blade to a supporting structure, the Huid-directing portion comprising a tubular sheath dening the fluid-directing surfaces thereof, the walls of the sheath abutting at least some of the laminae, the above-recited laminae being mutually spaced to deiine passages for a cooling uid extending lengthwise of the blade, the laminae comprising two interleaved sets, one set being the above-recited laminae and the other set being coniined to the attaching means portion of the blade.

24.Y A fluid-directing blade for turbomachines and the like, said blade having a duid-directing portion and cornprising a number of physically united laminae having extension in the directions lengthwise of-the bladeV and from face to face of the blade, said laminae extending beyond one end of the fluid-directing portion' of the blade to provide means for attaching the blade to a supporting structure, the fluid-directing portion comprising a tubular sheath defining the fluid-directing surfaces thereof, the walls of the sheath abutting at least some of the laminae, the laminae being mutually spaced to dene passages for a cooling fluid extending lengthwise of the blade, the laminae comprising two interleaved sets, the laminae of each set being staggered with respect to adjacent laminae of the other set to provide the said passages between adjacent laminations of the other set.

France July 11, 1951 

